This invention relates to thermosyphon heat exchangers and an improved construction thereof which provides enhanced performance and easier manufacture.
A thermosyphon is a closed end tube, with evaporator and condenser sections, containing a working fluid which during operation exists in both liquid and vapor phases. When sufficient heat is applied to the bottom of the thermosyphon, a pool of liquid at the bottom of the thermosyphon begins to boil. Cooling the top end of the thermosyphon causes vapor generated from the boiling working fluid to condense on the walls of the condenser and, driven by the force of gravity, to drain back to the liquid pool at the bottom. Due to the fact that the working fluid is constantly close to its saturation temperature, the thermosyphon is very effective in transferring large amounts of heat across a small cross-sectional area with only a small drop in temperature.
Thermosyphons powered by gas burners have been successfully tested in home and industrial applications such as space heating. The thermosyphons proposed for these applications may include a series of finned tubes that are each evacuated, and then prior to their being sealed, charged with a working fluid such as water. In use, the tubes are placed with their evaporator sections in one chamber receiving combustion products of a burner. In that chamber, hot combustion gases are blown over the evaporator sections of the tubes. In another chamber, room air to be heated is blown over the condenser sections of the tubes to remove heat from the condensing working fluid.
Due to the chemical properties which govern the operation of thermosyphons, it is crucial to their effective operation that the tubes be evacuated prior to their being charged with working fluid. It is also very important that the inner surfaces of the tubes be kept meticulously clean so that the working fluid wets the evaporator, thereby maintaining a high heat transfer coefficient in this section of the thermosyphon, and so that no non-condensible gases are generated by contaminants during the operation of the thermosyphon.
As a result of these requirements, several problems exist with the manufacture and operation of known thermosyphons. First of all, pressure relief mechanisms, such as known pressure relief caps can have corrosion problems and are extremely unreliable. Both the cost and unreliability of the pressure relief mechanisms can generate equivalent high cost and unreliability in the thermosyphons manufactured using those devices. Secondly, after a thermosyphon tube has been evacuated and charged with a working fluid, it is necessary to braze an end cap on the open end of the tube in order to form a leak tight pressure vessel. This process can also be expensive and may result in contamination from the braze. When a thermosyphon tube is operated with contaminants on its inner surface--e.g., dirt, grease, or oil, several problem areas can arise. The contaminants can act to prevent the working fluid from wetting the evaporator which will thereby degrade the performance of the thermosyphon. Additionally, contaminants can generate non-condensible gases that also degrade thermosyphon performance.
It is therefore an object of the present invention to provide a thermosyphon which is easier and less expensive to manufacture than known thermosyphons.
It is also an object of the present invention to offer a thermosyphon which requires less maintenance provide its operating life than known thermosyphons.
It is yet another object of the present invention to provide a thermosyphon which does not require an inside surface which is meticulously clean.